Have yourself a scientific Christmas,May your teaching load be light!Next year maybe funding will not be so tight.Have yourself a scientific Christmas,Pipette your last lane …Don’t stir the reagents with that candy cane!

You’re done with your holiday shopping and ready to read about selective breeding of Christmas trees, right? Well, then the Molecular Ecologist has just the post for you. Or maybe you’d rather check out an old Denim and Tweed post about mistletoe population genetics?

Meanwhile, over at The Molecular Ecologist, I interviewed my old friend Stacey Dunn about a study of hers recently published in Science, which presents ten years of data to examine how A.J. Bateman’s principal of sexual selection — that males maximize their evolutionary fitness by mating with lots of females, but females maximize their fitness by mating with just one or a few carefully-chosen males — in pronghorn.

The National Bison Range pronghorn have been studied extensively by John [Byers] and his lab since 1981. Each spring, we captured nearly all fawns born in the population. During captures, we weighed, measured, sexed and tagged the fawns and took a tissue sample for genetic analysis. We genotyped each individual alive since 1999 at 19 microsatellite loci. We determined paternity for all fawns based on genotype. Maternity was known from fawn captures, but was also confirmed genetically. We then used that information to reconstruct a multi-generational pedigree of the pronghorn population.

This week over at Nothing in Biology Makes Sense, I’m taking a look at a much-heralded new journal article that purports to solve an evolutionary puzzle that has particularly personal interest to me: how same-sex sexual orientation could evolve in the face of its selective costs. Of course, I’ve previously discussed a long list of possible answers to this question — but the new paper suggests that the best solution may lie in the epigenetics of sexual development.

Epigenetics is an appealing explanation for same-sex attraction because we have, at best, a fuzzy picture of the genetic basis of sexual orientation. Homosexuality definitely “runs in families”. That is, people with gay or lesbian parents, siblings, aunts, or uncles are more likely to be gay or lesbian themselves; and pairs of identical twins, who share pretty much all their genetic code, are more likely to have the same sexual orientation than pairs of fraternal twins, who share only half their genes.

Yet more sophisticated methods to identify specific genes associated with sexual orientation have failed to find any consistent candidates. (Though, as a caveat, the only genetic association study [PDF] I’ve seen suffers from small sample size and considers a very small number of markers by modern standards.) Moreover, while identical twins share sexual orientation more than fraternal twins, they don’t share it with complete fidelity — only about 20% of gay men who are identical twins have twin brothers with the same orientation.

For an explanation of what exactly epigenetics is, a full description of the new study, my evaluation of it all, and even some gratuitous — if, I hope, educational — beefcake, you’ll have to go read the whole thing.◼

Ryan linked to some new discussion of a study I covered back in June. That paper found a major flaw in a 1948 study of Drosophila fruit flies that was the first to clearly support a component of sexual selection theory — the idea that males maximize their evolutionary fitness (i.e., the number of offspring they sire) by having many mates, but females maximize fitness by selecting just a single “best” mate.

The author of the 1948 study, A.J. Bateman, tracked the parentage of flies in his study — which was necessary to tally the offspring of each male and female fly — using visible “marker” mutations. The new study’s authors, Patricia Gowaty et al., tried to replicate Bateman’s experiment, and discovered that some of the marker mutations were so disabling to the flies that they almost certainly biased Bateman’s results.

That knocks the legs out from under Bateman’s experiment. But it doesn’t really deal a knockout punch to sexual selection, much less to evolutionary psychology. Yes, evo psych (especially the kind that I really despise) tends to default to Bateman’s “randy males/choosy females” model. But evo psych, which is primarily about the recent evolutionary history of human behavior, isn’t the same thing as sexual selection theory, which is about the evolution of mating systems in, well, pretty much anything that reproduces sexually.

And, in fact, new studies with better data do support Bateman’s model for other non-human animals. Just a couple weeks ago, Science published a very thorough study on pronghorn antelope that tracked the interaction of Bateman-style sexual selection and regular old natural selection over a decade. (One of that study’s coauthors, Stacey Dunn, is a personal friend — I’ll be running an interview with her over at The Molecular Ecologist next week.) That work is based on modern genetic markers, which have none of the drawbacks of Bateman’s method.

But all of this is sort of beside the point, as far as the rightness or wrongness of evolutionary psychology goes, since fruit flies and pronghorn aren’t humans. There’s a huge diversity of sexual expression across the animal kingdom, and it’s absurd to think that we can make any particular conclusion about recent human evolution based on what works for insects or ruminants.

If evolutionary psychologists would be wrong to use Bateman’s fruit flies to support a particular hypothesis about human sexuality — and they would be — then those of us who disagree with them don’t have any reason to crow about Bateman’s mistakes.◼

That carnival of advice based on personal experience from previous career stages? Yep, it’s online today at The Molecular Ecologist. Head on over for a heaping helping of introspection, snark, and (mostly) sober reflection from across the science blogosphere.◼